The present disclosure relates to, for example, a power transmitting device which transmits power in a non-contact manner, a non-contact power transmitting system, and a signal generating method.
In non-contact power transmission (so-called wireless power feeding), it is necessary to output a high-power sine wave signal from a power transmitting device. A device which generates such a sine wave signal is called a high-frequency power source. For example, in a low-frequency, low-output audio power amplifier or the like not demanding a power exchange efficiency from a high-frequency power source to a sine wave signal, it is easy to change the signal level of the sine wave signal output from the high-frequency power source. In a high-frequency, high-output high-frequency power source used in wireless power feeding demanding a high power exchange efficiency, however, it is difficult to change the output power. In general, therefore, an inverter which generates a square wave through a switching operation capable of obtaining a high efficiency with a simple circuit configuration is used in many cases.
For example, highly efficient high-frequency power sources applicable to a non-contact power transmitting system include a Class-E amplifier (Class-E inverter), a half-bridge inverter, and a full-bridge inverter (so-called H-bridge circuit).
An overview of a power transmitting device using a common high-frequency power source will be described with reference to FIG. 1. FIG. 1 is a schematic circuit diagram for describing a common high-frequency power source using a half-bridge inverter.
As an example of the simplest configuration, the power transmitting device illustrated in FIG. 1 includes, for example, a high-frequency power source 101 and a resonance circuit 104 (series resonance circuit) including a power transmitting coil 102 and a resonance capacitor 103. The high-frequency power source 101 uses a half-bridge inverter as a signal generator. Since the configuration of the half-bridge inverter is common, a detailed circuit configuration thereof is omitted. The high-frequency power source 101 generates a square wave signal as a high-frequency output signal, and supplies the square wave signal to the resonance circuit 104.
All of the above high-frequency power sources, however, are inverters which generate the square wave in accordance with a switching system. The square wave corresponding to the output signal of the inverters includes a large number of harmonics, which lead to unnecessary radiation from the power transmitting device.
Japanese Unexamined Patent Application Publication No. 2011-120216 discloses an antenna drive including a trapezoidal wave signal generating circuit which generates a trapezoidal wave signal from a square wave signal having a predetermined frequency and a trapezoidal wave signal amplifier circuit which amplifies and supplies the trapezoidal wave signal to an antenna load. In this antenna drive, the trapezoidal wave signal amplifier circuit supplies a positive-phase output signal and a reverse-phase output signal, which are reversed in phase from each other, to the opposite ends of the antenna load, to thereby double the voltage applied to the load.